The invention relates to an attaching device for attaching broadcast fertilizer spreaders to farm tractors, which has a frame equipped with coupling means for attachment to the toplink and power lift arms of the three-point power lift of the tractor, on which frame one secondary toplink and a pair of lower arms are pivotally mounted for connection to a broadcast fertilizer spreader driven from the tractor's power take-off shaft, one or both of said lower arms being a secondary lift arm which can be raised and lowered by means of a hydraulic jack.
An attaching device of this kind has been disclosed in German Petty Patent No. 70 19 086. This attaching device has a frame consisting of a lower crossbeam having coupling members for the lower lift arms of the tractor's three-point power lift and an upright support disposed thereon on which the coupling means for the attachment of the toplink of the three-point power lift, the secondary toplink, the secondary lift arms and the hydraulic jack of the secondary lift system are disposed.
Even though it is possible with this attaching device to use the broadcast fertilizer spreader both for the fertilizing of bare ground and for the late fertilizing of plants that have grown up, and at the same time to have ease in loading the hopper of the spreader, the design of the known attaching device as described above has the following disadvantages.
Since the middle area between the tractor and the mounted broadcast fertilizer spreader is largely occupied by the frame parts of the attaching device, the metering device or shutter of the spreader, especially when it is in the lowered position for use, can be operated from the driver's seat of the tractor only if the actuating means is of a complex and expensive construction involving a plurality of links and joints making it possible to bring the adjusting lever or levers externally around the attaching device to the tractor. A plurality of joints, however, results in inaccuracies of adjustment on account of the free play which they involved. If, however, the actuating means is of the simple design commonly used, having the adjusting lever or levers extending forward from a single bearing point, then the driver must get down from the driver's seat for each readjustment of the metering device and then get back up on it again, and in any case he must do this at each end of the field in order to close and reopen the metering device or shutter.
Furthermore, in accordance with the explanations and drawings given in the Petty Patent, it is for the same reason necessary that the driving mechanism for powering the broadcast spreader be passed around the middle part of the attaching device. For this purpose it consists of a Cardan shaft, a countershaft mounted especially on the lower part of the attaching device, a complete chain or belt drive, and a chain or belt tensioning device not further explained or represented. This tensioning device must have a large range of action and therefore must be very complex, if the spreader is to be driven between the normal lowered position with the power lift arms raised and the secondary power lift arms lowered, on the one hand, and, on the other hand, the uppermost late fertilizing position in which the power lift arms of the tractor and the secondary lift arms are raised. The driving of the broadcast fertilizer spreader in a lower position (desirable for example for the spreading of dusty types of fertilizers) in which the secondary power lift arms are lowered and the tractor power lift arms are raised only about half-way, is not possible despite the complex construction of the drive mechanism, because then the countershaft of the attaching device and the spreader stubshaft are located approximately at the same height, so that the corresponding loosening of the chain or belt drive in this case can no longer be compensated by a tensioning device.